Methanogenesis Current Biology Zhe Lyu, Nana Shao, Taiwo Akinyemi, William B. Whitman  Current Biology  Volume 28, Issue 13, Pages R727-R732 (July 2018) DOI: 10.1016/j.cub.2018.05.021 Copyright © 2018 Elsevier Ltd Terms and Conditions

Figure 1 Sources of biological methane emissions to the atmosphere. Methanogens are found in a wide range of habitats, where they actively contribute 70% of the 500–600 Tg of methane introduced to the atmosphere each year. Percentages are the contributions of each habitat to the biological portion of the global methane emission budget. The ecology of each habitat largely determines the dominant substrates and probably selects for the types of methanogens found therein. Hydrogenotrophic methanogens are found in -rich habitats, aceticlastic methanogens in acetate ()-rich habitats, and methylotrophic methanogens in habitats rich in methyl compounds (). Current Biology 2018 28, R727-R732DOI: (10.1016/j.cub.2018.05.021) Copyright © 2018 Elsevier Ltd Terms and Conditions

Figure 2 The three enzymatic pathways of methanogenesis. All methanogenic pathways contain three common steps: the transfer of the methyl group to coenzyme M (CoM-SH), the reduction of methyl-coenzyme M with coenzyme B (CoB-SH), and the recycling of the heterodisulfide CoM-S-S-CoB. , CO2-reducing pathway; , aceticlastic pathway; , methylotrophic pathway; Abbreviations: MFR, methanofuran; H4MPT, tetrahydromethanopterin; H4SPT, tetrahydrosarcinapterin; ΔG0’, standard free energy change; CH3-R, methyl-containing compounds such as methanol, methanethiol, dimethylsulfide, monomethylamine, dimethylamine, trimethylamine, and tetramethylammonium; Fdred, reduced form of ferredoxin; Fdox, oxidized form of ferredoxin; ΔμNa+, electrochemical sodium ion potential; ΔμH+, electrochemical proton potential; FBeB, flavin-based electron bifurcation; CDeT, cytochrome-dependent electron transfer; MCR, methyl-coenzyme M reductase; CODH/ACS, carbon monoxide dehydrogenase/acetyl-CoA synthase/decarbonlyase complex. Current Biology 2018 28, R727-R732DOI: (10.1016/j.cub.2018.05.021) Copyright © 2018 Elsevier Ltd Terms and Conditions

Figure 3 Methanogens in the evolutionary tree of Archaea. Schematic phylogeny of the Archaea based upon a concatenation of 122 conserved marker proteins contains at least 11 ancient lineages or phyla (suffix -ota). So far, methanogens have been found in the four bolded phyla, namely the Euryarchaeota, Crenarchaeota, Halobacterota, and Thermoplasmatota, all of which likely evolved from a common methanogenic ancestor. The Candidatus taxa, abbreviated prefix Ca., have been observed in metagenomic sequences of environmental samples but never isolated in culture. The taxonomical classification at the phylum level follows a standardized taxonomical structure proposed at http://gtdb.ecogenomic.org/tree. The nomenclature is still not fully resolved, and additional phyla have been proposed. Trophic types of methanogenesis for each methanogen class (suffix -ia), order (suffix -ales) or family (suffix -aceae) are listed in the parentheses: H2, hydrogenotrophic; Ac, aceticlastic; Me, methylotrophic methanogenesis. Current Biology 2018 28, R727-R732DOI: (10.1016/j.cub.2018.05.021) Copyright © 2018 Elsevier Ltd Terms and Conditions